a. Field of the Invention
This invention relates to a process for continuously culturing adherent animal cells, and more specifically, to a process for continuously culturing adherent animal cells in suspension.
b. Description of the Prior Art
Culturing of cells in large quantities on an industrial scale is a technique which is important in the production of various hormones, enzymes, lymphokines, nucleic acids, antibiotics and other useful biologically active substances. In many cases, cells producing these biologically active useful substances, particularly transformed cells having inserted DNA so as to permit secretion of the desired substances are adherent, and it is an industrially important problem to develop a technique of efficiently culturing these cells.
Some methods of culturing large amounts of adherent cells and devices therefor have previously been proposed. Many of them, however, are directed to the growth of the cells adhering to the surface of a solid carrier, and give rise to problems in regard to scale-up, operability and stability in long-term continuous operation. For example, the microcarrier culturing method developed by Van Wezel is excellent and involves culturing cells on microcarriers whereby they can be cultured in suspension in a tank [see Growth of Cell Strains and Primary Cells on Microcarriers in Homogeneous Culture, Nature 216, 64-65 (1967)]. However, according to the culturing method of Van Wezel et al., the culture area depends upon the area of the microcarrier, and when the culturing is continued for a long period of time, the cells are gradually come off from the microcarriers.
U.S. Pat. No. 4,059,485 describes an attempt to culture adherent cells in suspension in a serum-containing medium. This method, however, has the disadvantage that as the culture is continued, the adherent cells aggregate to form large masses, and the cells in the large masses necrotize.
To the best of the knowledge of the present inventors, there has been no industrial technique of culturing adherent animal cells in suspension by themselves continuously over long periods of time without forming large aggregated cell clumps.
c. Objects of the Invention
It is an object of this invention to provide a process by which adherent animal cells can be cultured in suspension without using solid carriers such as microcarriers.
Another object of this invention is to provide an industrial process by which adherent animal cells can be cultured in suspension continuously over long periods of time.
Still another object of this invention is to provide an industrial process by which adherent animal cells can be cultured continuously over long periods of time while maintaining the cells themselves or relatively small aggregated particles in suspension.
Yet another object of this invention is to provide a process by which adherent animal cells can be cultured in suspension in a very high density.
A further object of this invention is to provide a process by which adherent animal cells can be cultured in suspension by using a serum-free culture medium.
A still further object of this invention is to provide a process by which adherent animal cells which secrete a useful biologically active substance are cultured in suspension, the culture broth is taken out from the culture tank, and the useful biologically active substance is recovered continuously and stably from the culture broth.
Additional objects of the invention will become apparent from the following description.